Gaseous halo-sulfonic acid anhydride catalysts for curing furfuryl alcohols and furan resins

ABSTRACT

HALOGENATED SULFONIC ACID ANHYDRIDES (E.G. TRIFULOROMETHYL SULFONIC ACID ANHYDRIDE) ARE USED TO CURE FURFURYL ALCOHOL OR FURAN RESINS, OPTIONALLY CONTAINING A SILANE. THE METHOD FINDS PARTICULAR UTILITY WHERE THE RESINS ARE USED AS FOUNDRY CORE BINDERS, SINCE THE CATALYST CAN BE INTRODUCED IN GASEOUS FORM, AT ROOM TEMPERATURE.

United States Patent 3,639,654 GASEOUS HALO-SULFONIC ACID ANHYDRIDE CATALYSTS FOR CURING FURFURYL ALCO- HOLS AND FURAN RESINS Janis Robins, St. Paul, Minn., assignor to Ashland Oil, Inc. No Drawing. Filed Mar. 10, 1969, Ser. No. 805,817 Int. Cl. B22c 1/22; C08g 13/00, 51/04 US. Cl. 260-37 R 9 Claims ABSTRACT OF THE DISCLOSURE Halogenated sulfonic acid anhydrides (e.g. trifluoromethyl sulfonic acid anhydride) are used to cure furfuryl alcohol or furan resins, optionally containing a silane. The method finds particular utility where the resins are used as foundry core binders, since the catalyst can be introduced in gaseous form, at room temperature.

This invention relates to a novel method of curing binder compositions and, more particularly, to the room temperature curing of binder compositions which are useful in the production of foundry cores. Even more specifically, this invention relates to combinations of a foundry aggregate such as sand, a binder such as furfuryl alcohol or a furan resin, and the treatment thereof with a gaseous catalyst capable of effecting curing at room temperature.

In the foundry art, cores for use in making metal castings are normally prepared from mixtures of an aggregate material, such as sand, which has been combined with a binding amount of a polymerizable or curable binder. Frequently, minor amounts of other materials are included in these mixtures (e.g. iron oxide, ground flax fibers, and the like). The binder permits such a foundry mix to be molded or shaped into a desired form and thereafter cured to form a self-supporting structure.

Typically, sand is used as the aggregate material. After the sand and binder have been mixed, the resulting foundry sand mix is rammed, blown, or otherwise introduced into a pattern, thereby assuming the shape defined by the adjacent surfaces of the pattern. Then, by the use of catalysts and/or the use of heat, the polymerizable or curable binder is caused to harden, thereby converting the formed, uncured foundry sand mix into a solid, cured core. This hardening can be accomplished in the original pattern, in a gassing chamber, or in a holding pattern. US. 3,145,438 and 3,121,368 are illustrative of prior art techniques.

In an effort to prepare cores without the necessity of using heat, attempts have been made at the preparation of various binder-curing agent compositions which would be capable of curing, at room temperature, i.e. at temperatures from about 45-120 F. and more commonly about 6090 F. A number of such combinations have been developed or suggested but have been found to suffer from one or more deficiencies. Typical of the deficiencies exhibited by prior art binder systems alleged to cure at room temperature have been a lack of the property of rapidly imparting tensile strength, intolerably short bench life of the mix, high toxicity, inability to combine well with all foundry aggregates, high sensitivity to moisture, contamination of surface of casting, giving rise to creation of pin holes in the castings and production of the undesirable and sometimes corrosive products.

3,639,654 Patented Feb. 1, 1972 "ice It is, therefore, an object of the present invention to provide a novel binder system and a process for curing the binder system at room temperature. -It is another object of this invention to provide a foundry binder system characterized by its ability to rapidly cure, at room temperature, when used in foundry mixes and which, in addition, exhibits one or more of the following properties:

(A) High tensile strength;

(B) Adhesion to commonly used foundry aggregates;

(C) Ability to impart excellent degree of moldability or plasticity to foundry sand mixes;

(D) Realistic bench life independent of curing rate; and

(E) Ability to form cores which result in excellent castings by reducing or eliminating the general problems of conventional air-drying binders, surface cracks, and surface contamination.

It is a further object of the present invention to provide a process for producing cores and other foundry shapes from foundry mixes incorporating the novel binder system of the present invention.

Still another object of the present invention is to provide foundry products containing the binder systems of the present invention in cured form.

Other objects will be apparent from the following description and claims.

Briefly, the binder systems of this invention depend on conventional binding materials such as furfuryl alcohol, furan resins and mixtures thereof. The novel features of this invention lie in the curing agents which are utilized and their application in gaseous form. The curing agents of this invention are halogenated sulfonic acid anhydrides containing up to two carbon atoms and having a boiling point at atmospheric pressure of up to about 200 C. The halogens can be fluorine, chlorine, or bromine, and preferably are fluorine or chlorine. The preferred curing agents are those which are gaseous or which are volatile liquids at atmospheric pressure at 45-120 F.

Suitable sulfonic acid anhydride curing agents include the following:

Curing is accomplished by contacting the binder material with a gaseous stream of the curing agent. The gaseous stream can contain an inert carrier gas such as air or nitrogen. Typically, the portion of the catalyst is volatilized by an air stream at or near room temperature and the catalyst containing air stream is allowed to contact the sample to be cured. The carrier gas can, of course, be at an elevated temperature in order to more efficiently volatilize the catalysts which are less volatile.

Curing can be accomplished in a relatively short period of time (eg 15-30 seconds) and with certain of the binders disclosed herein, curing is evidenced by a darkening of the sand specimen. The catalyst treatment results in no white fumes or noxious residues as is the case with other known gaseous catalysts such as chlorine. The lack of formation of white fumes is one of the advantages of the present method and results from the relative stability to hydrolysis of the catalysts of this invention and their presumed conversion to non-volatile acids or esters when brought into contact with the binder material.

The binder materials capable of being cured by the catalysts and process of the present invention include furfuryl alcohol, furan resins and mixtures thereof. The furan resins are condensation products of furfuryl alcohol and aldehydes, particularly formaldehyde. These are wellknown materials and are commercially available. A preferred furan resin comprises an acid catalyzed reaction product of a molar excess of furfuryl alcohol with formaldehyde.

Although mixtures of furan resins and furfuryl alcohol have been found suitable in the invention, egg. mixture having a weight ratio of furfuryl alcohol to furan resin of from :90 to 90:10 parts by weight, a binder consisting of only furfuryl alcohol is preferred.

The binder composition can be modified with a minor proportion of a silane of the general formula wherein R is a hydrocarbon radical and preferably an alkyl radical of 1 to 6 carbon atoms; and R is an alkyl radical, and alkoxy substituted alkyl radical, or an alkylamino substituted alkyl radical, in which the alkyl groups contain 1 to 6 carbon atoms. A particular silane embraced by the above generic formula and found to be effective in the compositions of this invention is 'y-amino-n-propyltriethoxysilane.

The silane is preferably present in amounts of 0.1 to 3.0% by weight based on the binder material and contributes certain advantages, particularly in tensile strength of the shaped foundry products.

The preparation of foundry cores according to this invention follows the Well-known and conventional procedures. A suitable core material such as sand, zircon, alumina, or the like is thoroughly mixed with the binder, placed in a mold, and cured. Specifically in the practice of this invention, sand is thoroughly mixed with the binding agent which optionally and preferably contains the abovementioned portions of silane. The aggregate, e.g. sand, is usually the major constituent, and the binder portion constitutes a relatively minor amount, generally less than 10% and frequently within the range of 0.25 to about 5.0% based on the weight of the aggregate.

The invention may be more fully understood by reference to the following examples. All parts and percentages are by weight unless otherwise indicated. These examples are illustrative of certain embodiments designed to teach those skilled in the art how to practice the invention and to represent the best mode contemplated for carrying out the invention and are not intended to limit the scope of the invention in any way.

EXAMPLE 1 This example illustrates the curing of furfuryl alcohol, and the benefits obtained by addition of silane by the method of this invention employing sulfonic acid anhydride catalysts and compares these results with those obtained with conventional catalysts.

Wedron Silica 5010 sand was intimately mixed with 2.0% by weight of the binder material. The binder material was either furfuryl alcohol (PA) or furfuryl alcohol/ silane mixture as indicated in Table I below. The silane was Union Carbide A1100 'y-amino-n-propyltriethoxysilane) and constituted 1% by weight of the binder mixture. The resulting mixes were formed into standard AFS tensile test samples by using the standard procedure.

The test samples were cured by injecting 1 ml. of the liquid or gaseous catalyst into an air stream and purging the test sample for 30 seconds until a thorough cure was observed (darkening of the sample). Two of the catalysts, (CH SO O and (NO SOQ O, are solids and do not have sufficient volatility to be used as gaseous catalysts.

Tensile strengths of the samples are summarized in Table I below:

This example illustrates the curing of binder materials comprising mixtures of furfuryl alcohol/ formaldehyde condensates with furfuryl alcohol in accordance with the process of the present invention.

The procedure followed was as in Example 1 except that in each instance the binder was a mixture of Chem-Rez 300 (an acid catalyzed 1 /2 :1 molar condensation product of furfuryl alcoholzformaldehyde) and furfuryl alcohol. In runs 1 and 2, parts of Chem-Rez 300 and 50 parts furfuryl alcohol are used. In runs 3-6, 30 parts Chem-Rez 300 and parts furfuryl alcohol are used.

The presence or absence of silane and the tensile strength results are summarized in Table II below:

comprising furan resins (i.e. furfuryl alcohol/formaldehyde condensates) in accordance with the process of the present invention.

The procedure followed was as in Example 1 except that in each case the binder was Chem Rez 300 (an acid-catalyzed 1 /2 :1 molar condensation product of furfuryl alcohol formaldehyde) The tensile strengths are summarized in Table Ill below:

TABLE III Tensile strength (p.s.l.)

Catalyst 1% silane Immediate 1 hour 24 hours CF SOg)zO. N0 1 70 190 1 50 200 175 The curing agents of this invention can also be incorporated directly into the binder material. Depending on the particular binder-catalyst combination and its cure rate, if may be necessary or desirable to inactivate the catalyst. This can be done, for instance, by adsorption of the catalyst on a molecular sieve or by its encapsulation in an inert material, for release as desired.

The invention has been illustrated with reference to a particular application. Numerous other applications of the process of curing a binding agent in accordance with this invention will occur to those skilled in the art. The process of this invention can be utilized in a variety of instances where a binder or impregnant is applied to a substrate and is to be cured. Examples include the production of coated paper, corregated board, sandpaper, emery cloth, and grinding wheels.

It will be apparent that a number of changes can be made in the process illustrated in the examples without departing from the scope of the invention as the examples are deemed merely illustrative and not comprehensive of the invention.

Although the invention has been described in considerable detail with reference to certain preferred embodiment thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described above and as defined in the appended claims.

What is claimed is:

1. A process for curing a binder material deposited on a substrate, said binder material selected from the group consisting of furfuryl alcohol, a furan resin which is a condensation product of furfuryl alcohol and an aldehyde, and mixtures of furfuryl alcohol and such a furan resin, said process comprising contacting said binder material with a gaseous halogenated sulfonic acid anhydried containing up to 2 carbon atoms and having a boiling point at atmospheric pressure of up to about 200 C., for a time sufiicient to effect curing.

2. The process of claim 1 wherein said binder material contains, in addition, a minor proportion of a silane having the formula R'O-SIR RO/ wherein R' is an alkyl radical of 1 to 6 carbon atoms; R is an alkylamino substituted alkyl radical, in which the alkyl groups have 1 to 6 carbon atoms.

3. The process of claim 2 wherein the silane comprises 0.1 to 3% by weight of the binder material.

4. The process of claim 3 in which the silane is 'y-aminon-propyltriethoxysilane.

5. The process of claim 4 wherein the substrate is particulate material.

6. The process for preparing shaped foundry products which comprises (a) forming a foundry mix by uniformly distributing on a foundry aggregate containing sand as the major constituent, a binding amount based on the weight of the aggregrate of a binder material selected from the group consisting of furfuryl alcohol, a furan resin which is a condensation product of furfuryl alcohol and an aldehyde and mixtures of furfuryl alcohol and such a furan resin;

(b) shaping the foundry mix in a mold; and

(c) contacting the shaped foundry mix with a gaseous halogenated sulfonic acid anhydride containing up to 2 carbon atoms and having 'a boiling point at atmospheric pressure of up to about 200 C., for a time sutficient to effect curing.

7. The process claim 6 wherein said binder material contains, in addition, a minor proportion of a silane having the formula wherein R is an alkyl radical of 1 to 6 carbon atoms; R is an alkylamino substituted alkyl radical, in which the alkyl groups have 1 to 6 carbon atoms.

8. The process of claim 7 wherein the silane comprises 0.1 to 3 by weight of the binder material.

9. The process of claim 8 wherein the silane is -aminon-propyltriethoxysilane.

References Cited UNITED STATES PATENTS 2,732,398 1/1956 Brice et a1. 260-503 2,805,249 9/1957 Gilbert et al 260-505 3,145,438 8/1964 Kottke et al 22193 3,184,814 5/1965 Brown 22193 3,220,970 11/1965 Carlstriim et a1. 260-37 FOREIGN PATENTS 575,583 5/1959 Canada 26067 DONALD E. CZAIA, Primary Examiner H. S. COCKERAM, Assistant Examiner US. Cl. X.R.

16416, 43; 260-67 FA, 88.5, DIG. 40 

